1. Field of Invention:
This invention relates generally to laser beam systems for carrying out surgical procedures, and more particularly to a system using a carbon dioxide laser whose collimated laser beam is conducted through a cannula to an outlet section where the beam is directed by a reflective deformable membrane toward the surgical site, the membrane being controllable to assume a concave form which optically focuses the beam at a target surface on the site.
2. Status of the Art:
Throughout the course of modern surgery, the desideratum has always been for a technique by which one can execute the surgical procedure of interest in a manner optimizing operating room time and surgical effect while minimizing tissue trauma and bleeding as well as the period during which the patient is under anesthesia.
With the advent of miniaturized arthroscopic instruments, orthopaedic surgeons are now able to perform delicate operations in a relatively short time that were not heretofore feasible. An arthroscope is a cannula whose diameter is small enough to enter interstices between the bones in a joint to create a body entry which is small compared to that normally required in a cold knife procedure. By using a miniature rotary cutter that slides into the cannula, the surgeon is able to debride tissue fragments that are responsible for joint deterioration, disease and arthritis.
The present invention deals with a system in which a laser beam projected through an arthroscope functions as a non-mechanical surgical tool. The use of laser energy in medicine is now commonplace. Laser beams are used, for example, in skin treatment, in eye repair and in surgery. The main concern of the present invention is with surgical applications in which a high power laser beam functions to both cut and cauterize and must therefore be focused onto the surgical target.
Ordinary light is non-coherent and is made up of random and discontinuous wavelengths and phases of varying amplitude. The principle characteristic of a laser beam lies in its coherence, which means that corresponding points in its wavelength are in phase. In surgical applications, lasers in current use are the Nd:YAG, the CO.sub.2 and the Argon laser. In practice, the laser may be pulsed or continuous.
Laser light is usually more intense, more monochromatic and more highly collimated than light from ordinary sources such as tungsten-filament lamps. The intensity of laser light can be extremely high. Thus power densities of over 1000 MW/cm.sup.2 are obtainable to produce a beam capable of cutting through and vaporizing solid materials. Lasers fall into four basic categories: solid state-optically pumped; liquid dye; semi-conductor; and gas. Together, these four laser types cover the spectral region extending from ultraviolet to infrared.
The present invention will be described chiefly in the context of knee surgery, for meniscectomies and synovectomies are among the most frequently encountered surgical problems for which arthroscopic surgery is the appropriate solution. It will, however, be recognized that the surgical applications are by no means limited to these procedures, and that the invention is useful wherever the need exists to direct a focused CO.sub.2 laser beam toward a surgical site in a path other than line-of-sight. The invention is also useful in those industrial applications which require a steerable and focusable laser beam.
Though standard arthroscopic techniques employing miniature surgical cutting tools yield good results, they have been hampered by difficulties encountered in tool miniaturization and in site designation during the surgical procedure. Due to size constraints the accuracy with which miniature tools can be manipulated and placed has imposed practical limits on arthroscopic surgery.
A carbon dioxide laser has distinct advantages over other types as an effective surgical tool, for it cuts a visible and extremely clean line with very little backscatter, and it is capable of applying enormous amounts of energy onto a tissue site, thereby vaporizing the tissue into its gas constituents and leaving no biological residue. Because a CO.sub.2 laser beam can vaporize any biological target such as cancer cells, it creates an absolutely sterile wound site devoid of biological contaminants. Moreover, the CO.sub.2 laser lends itself to a precise level of control and can therefore be set to cut through one cell layer at a time in almost any cell substrate, or to burn through several millimeters of hard tissue, whichever procedure is indicated.
Despite its marked advantages over other types of lasers, the use of a CO.sub.2 laser beam has hitherto been unavailable in arthroscopic surgery, for a CO.sub.2 beam cannot be conducted through a fiber optic conduit. A CO.sub.2 laser beam has a wavelength of 10.6 micrometers which lies in the infrared region of the spectrum and is therefore too long to be transmitted through existing fiber optic light conduits. As a consequence, the CO.sub.2 laser in the field of surgery has heretofore been limited to those applications which do not make use of a fiber optic conduit for conducting the laser beam.
In arthroscopic surgery, the usual practice is to employ a cannula having a 3-5 millimeter diameter. If one seeks therefore to integrate a CO.sub.2 laser with an arthroscope to perform surgery on a joint such as the knee, the requirements of the surgical procedure then dictate that the laser beam be orientable and be capable of travelling around corners. Beam steering expedients such as motorized lenses and rotating mirrors are not only expensive, but they are difficult to incorporate in a small bore arthroscopic cannula. As a consequence, use has not previously been made of a CO.sub.2 laser in knee surgery.
In arthroscopic surgery, the object is to remove tissue particles from joints (meniscectomies and synovectomies--i.e., removing tendril-like particles of the meniscus and synovia). In other types of surgery such as in prosthetic hip, shoulder and knee implants, the aim of the procedure is to debride and polish particular areas of bone or tissue to create a socket whereby the prosthesis can then be driven into a precisely contoured socket.
In order to carry out orthopaedic surgery in soft or hard tissue with a laser beam, the operating surgeon must know just where cutting is taking place. The surgeon does not have a scalpel in his hand as a cutting tool; hence it is only by visual observation that he can sense his laser incisions, not by tactile sensation. Nd:YAG and Argon types of lasers make it difficult for surgeons to accurately evaluate the parameters of their incisions, for these have a short wavelength and exhibit backscatter characteristics. Backscatter or distal tissue penetration, is a phenomenon experienced when a laser beam having a short wavelength impinges on a visible target surface, the beam penetrating the target to a depth beyond that which can be visually observed. This penetration in depth heats and volatilizes the tissue in the backscatter region underlying the exposed target surface which is the only visible area of impact. This region assumes a non-linear geometric form that is a function of the type of cells and tissue which border one another in the region subject to backscatter effects.
An Argon laser is centered at about 0.512 micrometers in the wavelength spectrum, while that of an Nd:YAG laser is centered at about 0.532 micrometers. These shorter wavelengths are comparable to ultraviolet or blue-green light at the upper end of the light spectrum, as opposed to infrared radiation at the lower end. As a consequence, an Nd:YAG or an Argon laser beam will penetrate flesh, tissue and water, the beam transferring its energy to pigmented tissues beyond the surface of beam impingement. Because of the backscatter experienced with Nd:YAG and Argon laser beams, this gives rise to deleterious tissue destruction.
In contradistinction, a CO.sub.2 laser generates a long wavelength beam having a 10.6 micrometer wavelength which lies in the infrared portion of the light spectrum. The energy of a CO.sub.2 laser beam is fully absorbed by water and therefore by cells composed mostly of water. As a consequence, those cells in the target surface which are directly exposed to a focused CO.sub.2 laser beam are the only ones destroyed, for there is virtually no backscatter. The energy transmitted to the focal point is almost entirely absorbed by the water in the local cells, and the energy penetrating the region beyond this point is at a very low and innocuous level.
As noted previously, in arthroscopic surgery, the usual practice is to use a cannula having a 3-5 millimeter diameter. If one attempts to integrate a CO.sub.2 laser with an arthroscope to perform surgery in joints such as the knee, the requirements of the procedure dictate a steering action by which one is able to direct the laser beam around corners toward the site of interest. While a flexible fiber optic conduit is capable of directing light conducted therethrough in any desired direction, a conduit of this type is not useable with a long wavelength CO.sub.2 laser beam. And though it is possible to steer a CO.sub.2 laser beam with rotating mirrors and motorized lenses, these expensive expedients are difficult to incorporate in a small bore cannula.
3. Prior Art:
The patent to Swope discloses a photo-coagulation technique in which the beam from a gas laser is directed by an optical system created by a series of mirrors to the site to be treated. In the Kawaski U.S. Pat. No. 4,174,154, a condenser lens and a series of mirrors is used in conjunction with a CO.sub.2 laser beam to direct the beam to a desired site. In the CO.sub.2 laser beam endoscope shown in the Worster U.S. Pat. Nos. 4,211,229 and 4,141,362, a lens system is used to bring the beam to a focus. The Frank U.S. Pat. No. 4,313,431 makes use of fiber optics in an endoscope to conduct a laser beam.
The U.S. Pat. No. to Bredemeier 3,796,220 shows a stereo laser endoscope using a CO.sub.2 laser which is focused by means of a lens and a reflecting mirror to provide a fixed focus system, the lens being so chosen as to focus the laser beam on a point lying in the focal plane of a microscope.